Roller assemblies which are removably mounted on carriers attached to the floor of a vehicle are widely used for conveying cargo within such vehicles. These roller assemblies or “actuators” are intended for use in systems which involve the transport of commercial and military cargo containers commonly used in the air cargo, ground cargo (trucking), rail cargo and shipboard cargo industries. The actuator installs into a cargo transport vehicle, and provides motive force and holding (i.e., braking) for the containers within the vehicle.
The actuator, commonly called a power drive unit or powered drive unit (PDU), works in conjunction with external support equipment to facilitate the loading and unloading of the cargo containers into and out of the vehicle. The PDU typically incorporates a fixed frame or support base rigidly attached to the floor or floor structure of the cargo vehicle. A moving drive assembly is attached to the support base. The drive assembly includes drive roller or rollers for contacting the cargo containers and providing motive force to them by means of the frictional coefficient between an elastomeric roller surface and the container bottom, and a motor for rotating the drive roller. Cargo container bottoms are generally smooth, metallic coverings attached to a square or rectangular frame structure; however, they may also be made of non-metallic material such as wood or reinforced plastic.
The PDU also incorporates a lift mechanism which raises the drive assembly from its lowered position into abutment against the cargo container bottom, as by rotating cams on a common camshaft against reaction points or bearings in the support base. The lift mechanism provides the vertical force to the drive roller, which in turn provides the frictional force to drive the container. The lift mechanism also can be engaged to hold the container in place when the drive roller is not turning, to prevent the unintended motion of containers in the vehicle.
When drive and/or hold commands are removed from the PDU, the PDU drive assembly lowers to its retracted position. The cargo containers are typically supported by a plurality of free turning cylindrical rollers, ball transfer units or caster assemblies, which are collectively referred to as the conveyance hardware. When the PDU is retracted, the containers are free to move on the conveyance hardware, and are typically held in position during vehicle motion by latches, guides and other restraint hardware.
In areas requiring movement of containers in mutually perpendicular directions, such as a doorway area where containers need to move both laterally and longitudinally in a cargo vehicle, steerable PDU's are employed which rotate upon application of an external command, to orient the drive assembly in the required direction and to drive the cargo containers. Typical steerable PDUs are described in U.S. Pat. No. 3,978,975, and U.S. Pat. No. 4,589,542, both of which are incorporated herein by reference.
Prior art PDU's can involve complex mechanisms which are heavy, costly and difficult to repair or replace. However, regardless of their degree of complexity, prior art PDU's are limited in their operational flexibility under varying conditions, such as use in different vehicles or for different types of cargo containers or loading. As a result, they are not easily adaptable to different applications.